Referring initially to FIG. 1, a prior art percussion drill bit 10 is shown having a bit head 12 that includes a bit face 14 and a multitude of inserts 20 for impacting and fracturing the earthen formation (not shown). Inserts 20 were typically disposed on various portions of the bit face 14. For example, inserts 20 are shown disposed on the central portion 19 of the bit face 14 in the proximity of the central axis 13 of the bit 10, and other inserts 20 are disposed in numerous circumferential rows 70 on the bit face 14, such as a first row 72, second row 74, third row 76 and gage row 78. The term “gage row” as used herein refers to the row 70 extending around, or adjacent, the periphery, or edge, 15 of the bit face 14. All of the inserts 20 on the bit face 14 of the prior art hammer bit 10 had substantially the same geometric shape and size, such inserts 20 being referred to herein as “small” inserts 22. Typically, such inserts 22 had a diameter of 0.75 inches or smaller. The bit face 14 also included one or more fluid flow openings 16 and flow channels 18 for allowing the flow of circulation fluid (not shown) from within the bit 10 to the exterior 44 of the bit 10.
Different places on the bit head may see different conditions during drilling yet the same inserts typically are used at all places of the bit head of the prior art. A need exists for a drill bit with different inserts at different places on the bit head to better match the varying conditions or applications of different places on the bit head.